The present invention provides, in a first aspect, a video camera system comprising: a video sensor providing image data; a low power imminent event detector coupled to the sensor which receives the image data from the video sensor and processes the received image data to detect changes in the image data and thereby detect an imminent event and produces an event signal on detection of an imminent event; and a main event processor also coupled to the video sensor to receive the image data, the main event processor being a higher power device than the imminent event detector, the main event detector having a dormant mode in which the main event detector consumes little or no power and a fully active powered up mode, wherein: the main event processor switches from the dormant mode to the fully active mode in response to the event signal; the main event processor when fully active processes the image data from the sensor and analyses the processed image data to extract information therefrom; and the imminent event detector is arranged such that it does not produce the event signal when the changes in the image data are large, thereby indicating only that the sensor is moving.
The present invention provides, in a second aspect, a method of detecting an imminent event, comprising: receiving pixel values from the sensor for a plurality of video fields; generating a difference value by comparing the pixel values of the same location in different video fields; increasing a difference count when the difference value is above a difference threshold; comparing the difference count with a noise threshold, below which indicates noise; and comparing the difference count with a movement threshold, above which indicates sensor movement; wherein if the difference count is between the noise threshold and movement threshold the event signal is generated indicating an imminent event.
Thus, the video camera system has a low power consumption. The camera system operates at full power only intermittently. This can increase the lifetime of the illumination source. This can also reduce the heat generated within the camera system. Further, this can allow use of a solar panel to power the camera system.